a. Field of the Invention
The present invention relates to power control circuits for televisions and, more particularly, to a standby power circuit for televisions.
b. Description of the Prior Art
In today's digitally controlled television sets, it is generally desirable to maintain a small amount of power to some of the ICs, e.g. to preserve memory, and IR remote capabilities. It is preferable that standby power be approximately 5 watts and, more preferably approximately 3 watts.
While there are various types of circuits used in televisions, one type is known as the "hot" type chassis. "Hot" type television chassises do not require isolation in the off-the-line supplies, as isolation is achieved at the antenna input in this type of product. Thus, standby power is achieved by deriving power directly from the line (1/2 wave or full-wave bridge) and dropping the level through an impedance to the appropriate level needed by the standby circuits. However, this method is inefficient.
In a bus-controlled television system, a microprocessor sends an "on" command via a "T-bus" to a bus-controlled television IC (also known as a T-chip), such as an LA7610 manufactured by Sanyo. The T-chip performs many processing functions needed for color television including e.g. IF, chroma, luma, audio, horizontal and vertical. Bus receivers needed to decode the "on" command must be supplied by a power source that is not dependent on the horizontal circuits for power, since the horizontal circuits are not powered until necessary. There is also the need to power the microprocessor and IR receiver. Such circuits typically use a 7.6 volt standby circuit of the T-chip. However, running all of these circuits off of the standby power of the T-chip takes a current of approximately fifty milliamps resulting in a standby power of nearly ten watts. Since the T-chip is responsible for about half of this power drain in order to power the 7.6 volt standby circuit, it is desirable to switch off the power to the T-chip until the power is needed, i.e. a short time before the horizontal circuits are to be engaged.
It is thus an object of the present invention to provide standby power for a bus controlled television set that is not derived from the T-chip.
It is another object of the present invention to provide a switching circuit for a the T-chip within a bus controlled television set.
It is further an object of the present invention to provide a switching circuit for a T-chip and standby power system within a bus controlled television set.